title: Nanocrystalline Nd2Fe17 synthesized by high-energy ball milling: crystal structure, microstructure and magnetic properties.
abstract: Nanocrystalline Nd(2)Fe(17) powders have been obtained by means of high-energy ball milling from nearly single-phase bulk alloys produced by arc melting and high temperature homogenization annealing. The rhombohedral Th(2)Zn(17)-type crystal structure of the bulk alloy remains unaltered after the milling process, with almost unchanged values for the cell parameters. However, the severe mechanical processing induces drastic microstructural changes. A decrease of the mean crystalline size down to around 10 nm is observed, giving rise to a considerable augmentation of the disordered inter-grain boundaries. This modification of the microstructure affects the magnetic behaviour of the milled powders, although the magnetic structure remains collinear ferromagnetic. While a unique ferro-to-paramagnetic transition temperature, T(C) = 339 ± 2 K, is observed in the bulk alloy, the nanocrystalline samples exhibit a more likely distribution of T(C) values. The latter seems to be responsible for the significant broadening of the temperature range in which magneto-caloric effect is observed, and the lowering of the maximum value of the magnetic entropy change.
authors.affiliation: Departamento de Física, Universidad de Oviedo, Calvo Sotelo, s/n, 33007 Oviedo, Spain. alvarezpablo.uo@uniovi.es
authors.forename: Pablo
authors.initials: P
authors.lastname: Álvarez
authors.forename: Pedro
authors.initials: P
authors.lastname: Gorria
authors.forename: Victorino
authors.initials: V
authors.lastname: Franco
authors.forename: Jorge
authors.initials: J
authors.lastname: Sánchez Marcos
authors.forename: María J
authors.initials: MJ
authors.lastname: Pérez
authors.forename: José L
authors.initials: JL
authors.lastname: Sánchez Llamazares
authors.forename: Inés
authors.initials: I
authors.lastname: Puente Orench
authors.forename: Jesús A
authors.initials: JA
authors.lastname: Blanco